The characteristics of semiconductor materials such as, for example, silicon, germanium and gallium arsenide and other semiconductors have been exploited to form a large variety of useful devices in the fields of electronics, communications, electro-optics, and nano-technology. In the field of semiconductor electronics, it is well established that formation of devices by utilizing strained-silicon can result higher carrier mobility and, thus, in superior device performance, including faster operation, higher current drive capability, and lower power dissipation.
Several approaches have been applied to produce suitably strained-silicon. These include formation of silicon films on mismatched crystalline lattice substrates, introducing larger or smaller atoms into the lattice, and mechanically applying tensile or compressive forces to silicon regions due to strains in adjacent regions. One particularly effective method has been the introduction of germanium atoms into a silicon lattice. Germanium atoms are larger than those of silicon and result in a strain of the predominately silicon lattice. Often germanium concentrations on the order of a few atomic percent to a few tens of atomic percent have been found useful in forming such silicon-germanium strained semiconductors.
Strained silicon materials for semiconductor device fabrication have been formed by blanket Si/SiGe epitaxy onto silicon substrates or by blanket transfer of strained-silicon layers onto insulator substrates for producing strained-silicon on insulator (sSOI) materials. Previous methods (such as epitaxy) for producing blanket strained-silicon on semiconductor or insulating (typically silicon oxide) substrates involve low throughput, high temperature, techniques that result in undesirably high costs per wafer.
In addition to the blanket techniques, there has been recent development of semiconductor devices enjoying the benefits of strained-silicon by using localized processing such as selective chemical vapor deposition to produce locally-strained semiconductor regions. Locally-strained techniques are useful, in part, because PMOS devices and NMOS devices benefit from having different strains in the strained-silicon channels of the devices, thus it is desirable to be able to control the amount and type (compressive or tensile) strain in local regions within a device or from device to device. Such local-strain techniques have also been expensive to implement and typically utilize high processing temperatures that can be a disadvantage in some applications.
Conventional ion implantation using atomic or molecular ions of materials containing germanium has not proven an efficient way of introducing germanium into silicon for creating strain. The required high concentrations of at least a few atomic percent of germanium in silicon for effective strain production require such high conventional ion implantation doses so as to be economically impractical with conventional ion implantation equipment.
For some semiconductor devices, it is desirable to dope the semiconductor material with, for example, boron at very high doping concentrations. In general, the solid solubility limit of the dopant in silicon has been an upper limit for effective doping. Past work indicates that the solid solubility limit of boron in silicon can be increased by introducing germanium atoms to the silicon.
The use of a gas-cluster ion beam (GCIB) for etching, cleaning, and smoothing surfaces is known (see for example, U.S. Pat. No. 5,814,194, Deguchi, et al.) in the art. GCIBs have also been employed for assisting the deposition of films from vaporized carbonaceous materials (see for example, U.S. Pat. No. 6,416,820, Yamada, et al.) As the term is used herein, gas-clusters are nano-sized aggregates of materials that are gaseous under conditions of standard temperature and pressure. Such clusters may comprise aggregates of from a few to several thousand molecules or more loosely bound to form the cluster. The clusters can be ionized by electron bombardment or other means, permitting them to be formed into directed beams of controllable energy. Such ions each typically carry positive charges of q·e (where e is the magnitude of the electronic charge and q is an integer of from one to several representing the charge state of the cluster ion). The larger sized clusters are often the most useful because of their ability to carry substantial energy per cluster ion, while yet having only modest energy per molecule. The clusters disintegrate on impact, with each individual molecule carrying only a small fraction of the total cluster energy. Consequently, the impact effects of large clusters are substantial, but are limited to a very shallow surface region.
Apparatus for creating and accelerating such GCIBs are described in the U.S. Pat. No. 5,814,194 patent previously cited. Presently available ion cluster sources produce clusters ions having a wide distribution of sizes, N, up to N of several thousand (where N=the number of molecules in each cluster—in the case of monatomic gases like argon, an atom of the monatomic gas will be referred to herein as either an atom or a molecule and an ionized atom of such a monatomic gas will be referred to as either an ionized atom, or a molecular ion, or simply a monomer ion.)